Trace element partitioning between NaNbO3 and CeFe3+O3 and kimberlitic and carbonatitic melts

Christopher Beyer

Perovskite is known to accommodate a wide range of incompatible elements (U, Th, REE, HFSE). The mineral is commonly found in the groundmass of silica-undersaturated ultramafic rocks and in carbonatites. In a previous study we have shown that CaTiO₃ perovskite (A²⁺B⁴⁺O₃-type) has strong control over the REE budget of kimberlites (Beyer et al. 2013).

Interestingly enough, perovskite has the potential to fractionate U from Th in silicate magmas (Figure 1). However, natural perovskites rarely consist of pure end-member CaTiO₃ (Chakhmouradian and Mitchell 2001). Perovskites usually forms a solid solution consisting of LREEFeO₃, lueshite (NaNbO₃), tausonite (SrTiO₃) and loparite (Na,Ree)Ti₂O₆, to name but a few (Mitchell et al. 2017).

Figure 1: Mineral/melt trace element partitioning coefficients of perovskite.

As an expansion of the current data set we will examine the effect of A¹⁺B⁵⁺O₃ and A³⁺B³⁺O₃ end members on the trace element partitioning between perovskite and melt. Experiments will be carried in a gas-mixing furnace to maintain control of the oxidation state of multivalent elements (i.e. Fe, Ce, Pb, U). The piston cylinder apparatus will be used to equilibrate perovskite with carbonatitic and hydrous kimberlitic melt. Trace element concentrations of the run products will be analyzed using laser ablation ICP-MS.

REFERENCES

Beyer C, Berndt J, Tappe S, Klemme S (2013). Trace element partitioning between perovskite and kimberlite to carbonatite melt: New experimental constraints. Chem Geol 353: 132-139

Chakhmouradian A, Mitchell R (2001). Three compositional varieties of perovskite from kimberlites of the Lac de Gras field (Northwest Territories, Canada). Mineral Mag 65: 133-148

Mitchell RH, Welch MD, Chakhmouradian AR (2017). Nomenclature of the perovskite supergroup: A hierarchical system of classification based on crystal structure and composition. Mineral Mag 81: 411-461 doi:http://dx.doi.org/10.1016/j.chemgeo.2012.03.025